Up to now, a large number of biodegradable films and sheets based on biodegradable resins such as polylactic acid and fatty acid polyesters and on natural materials such as starch have been proposed.
For example, Japanese Patent Application National Publication (Laid-Open) No. 10-511145-A (Patent Document 1) discloses a stretched film prepared from thermoplastic starch, a biodegradable polymer, cellulose fibers, and protein. JP 2002-371201-A (Patent Document 2) discloses a biodegradable film or sheet using a biodegradable resin such as polylactic acid, an inorganic filler such as calcium carbonate, and a water-soluble resin such as polyethylene glycol. JP 06-313063-A (Patent Document 3) discloses a biodegradable film wherein protein and a natural rubber are added as reinforcing agents to starch and a biodegradable fatty acid polyester.
JP 2003-292554-A (Patent Document 4) discloses a biodegradable film based on a biodegradable compound having active hydrogen such as starch with which a compound having an acryloyl group, urea, glycerine, and natural fibers such as cellulose are further used. JP 2003-105130-A (Patent Document 5) discloses a biodegradable film obtained from a composition prepared by crosslinking with a salt such as a calcium salt or aluminium salt, starch, urea and a compound having a carboxylic acid group such as carboxymethyl cellulose, and further adding glycerine and urea. JP 2004-339496-A (Patent Document 6) discloses a biodegradable film using starch, urea in an amount of 60 to 300% based on the starch, a polyhydric alcohol such as glycerine in an amount 10 to 150% by mass based on the starch, and natural materials such as paper or hemp fibers. JP 2001-288295-A (Patent Document 7) discloses a film using corn gluten meal, natural rubber, and urea as a plasticizer. Japanese Patent Application National Publication (Laid-Open) No. 2002-512929-A (Patent Document 8) describes a biodegradable film made of a composition containing starch, protein, natural cellulose fibers, a metal salt hydrate, and urea as a plasticizer.    Patent Document 1: Japanese Patent Application National Publication (Laid-Open) No. 10-511145-A    Patent Document 2: JP 2002-371201-A    Patent Document 3: JP 06-313063-A    Patent Document 4: JP 2003-292554-A    Patent Document 5: JP 2003-105130-A    Patent Document 6: JP 2004-339496-A    Patent Document 7: JP 2001-288295-A    Patent Document 8: Japanese Patent Application National Publication (Laid-Open) No. 2002-512929-A